1. Field of the Invention
The present invention relates to a CVD apparatus, and in particular, it relates to a CVD apparatus in which a uniform flow of reaction gas is established by exhausting the reaction gas from an equidistantly arranged gas exit and by minimizing a turbulence of the reaction gas to obtain a thin film of an averaged thickness to be deposited on a substrate.
2. Description of the Related Art
CVD apparatuses have been used in manufacturing semiconductor devices or else for depositing a thin film of, for example, an oxide or a nitride on the surface of a semiconductor substrate. In manufacturing semiconductor devices, it is desired to reduce a variation in the thickness of the deposited thin film.
FIGS. 9 to 11 of the attached drawings show a conventional rapid thermal CVD apparatus. FIG. 9 is a longitudinal cross-sectional view of the CVD apparatus, FIG. 10 is a cross-sectional view of the CVD apparatus along the lines b--b of FIG. 9, and FIG. 11 is a cross-sectional view of the CVD apparatus along the lines c--c of FIG. 9.
The CVD apparatus comprises a reaction chamber 1, a susceptor plate 3 fixed in the reaction chamber 1 for supporting a substrate 2 thereon and having an opening 3a at a substrate supporting region, and a reaction gas supply inlet 4 in the form of a shower nozzle for blowing a reaction gas from above the substrate 2 supported on the susceptor plate 3. Also, a source of infrared light 5 for heating the substrate 2 is arranged below the susceptor plate and an infrared light transparent window 6 is arranged between the source of infrared light 5 and the susceptor plate 3 for separating the reaction chamber 1 from an environment.
Also, a plurality of gas exits 7 are arranged circumferentially and equidistantly in the peripheral wall in the reaction chamber 1 at a level just above the susceptor plate 3 so that the reaction gas is exhausted uniformly and radially from the gas exists 7. A second gas supply inlet 8 for supplying a second gas such as nitrogen or an inert gas in the reaction chamber 1 is arranged between the susceptor plate 3 and the infrared light transparent window 6, and a second gas supply exit 9 is arranged at the same level as the second gas supply inlet 8. Accordingly, the reaction gas flows into the reaction chamber 1 above the susceptor plate 3 and the second gas flows into the reaction chamber 1 below the susceptor plate 3 independently of the reaction gas. However, there is an opening 10 in the peripheral wall of the reaction chamber 1; the opening 10 being connected to a loadlock chamber 12 via a gate valve 11 for inserting the substrate 2 in the reaction chamber 1 and discharging the substrate 2 from the reaction chamber 1. The opening 10 vertically extends from a portion above the susceptor plate 3 to a portion below the susceptor plate 3.
It is possible to deposit a thin film on the substrate 2 by maintaining the reaction chamber 1 at a vacuum level, heating the substrate 2 by the source of infrared light 5 and blowing the reaction gas to the substrate 2 from the reaction gas supply inlet 4. An undesirable reaction product may be deposited on the lower surface of the substrate 2 or the reaction gas may contaminate the infrared light transparent window 6 if the reaction gas enters the lower area of the reaction chamber 1 below the susceptor plate 3, and accordingly, the second gas flows in the lower area of the reaction chamber 1 below the susceptor plate 3 to prevent the reaction gas from leaking into the lower area beyond the susceptor plate 3 via a possible gap between the substrate 2 and the susceptor plate 3 and via the opening 10.
It is intended that the reaction gas flows uniformly from the reaction gas supply inlet 4 to the peripheral gas exits 7 to obtain a thin film of average thickness to be deposited on the substrate 2. However, the second gas, which does not serve the reaction, flows into the upper area of the reaction chamber 1 above the susceptor plate 3 via the opening 10, disturbing the intended uniform flow of the reaction gas and resulting in a less than average thickness of film deposited.